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vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 04 Jun 2021 03:02:18 +0000
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163
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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1 The data table that follows captures the results of this experiment:
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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2
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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3 * An FCDEV3B modem board was powered from a bench PSU whose output voltage
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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4 is controlled by an analog rotary knob;
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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5
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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6 * The PSU voltage knob was turned up and down to produce 0.1 V steps
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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7 from 3.2 V to 4.2 V;
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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8
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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9 * At each PSU voltage step, VBAT MADC reading was captured with an
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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10 mpr 30 command in fc-tmsh, and the actual voltage was measured with a
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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11 digital multimeter.
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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12
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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13 PSU voltage MADC reading Voltmeter reading
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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14 -------------------------------------------------
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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15 3.2 V 473 3207 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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16 3.3 V 488 3306 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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17 3.4 V 502 3403 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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18 3.5 V 517 3500 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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19 3.6 V 532 3597 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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20 3.7 V 546 3696 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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21 3.8 V 562 3804 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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22 3.9 V 576 3897 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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23 4.0 V 592-593 [1] 4003 mV
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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24 4.1 V 606 4.08-4.09 V [2]
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Mychaela Falconia <falcon@freecalypso.org>
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25 4.2 V 621 4.18-4.19 V [2]
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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26
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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27 [1] on the cusp of MADC step, got alternating readings
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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28
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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29 [2] My cheap multimeter's 4 V range was exceeded at this point, and I had
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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30 to switch to the next higher range in which only two digits after the
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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31 decimal point were displayed.
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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32
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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33 If we apply the firmware's default VBAT calibration values of A=7000 B=0,
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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34 we see that VBAT numbers computed from MADC readings are higher than the
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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35 true VBAT by 24 mV at the low 3.2 V end and by 45 mV at the high 4.2 V end.
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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36
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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37 Calibration math attempt from 3207 to 4003 mV, using MADC=592 at high end
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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38 =========================================================================
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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39
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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40 A=(4003-3207)/(592-473)*1024 = 6849
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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41
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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42 B parameter computed from each calibration point:
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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43
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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44 MADC reading Voltmeter reading Computed VBAT w/o B B parameter
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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45 ---------------------------------------------------------------------------
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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46 473 3207 mV 3163 44
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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47 488 3306 mV 3263 43
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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48 502 3403 mV 3357 46
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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49 517 3500 mV 3457 43
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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50 532 3597 mV 3558 39
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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51 546 3696 mV 3651 45
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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52 562 3804 mV 3758 46
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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53 576 3897 mV 3852 45
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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54 592 4003 mV 3959 44
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55
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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56 B values range from 39 to 46, a very small variation - thus the behaviour of
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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57 VBAT MADC really does fit the linear model, and linear calibration really does
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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58 work well.
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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59
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
Mychaela Falconia <falcon@freecalypso.org>
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60 Calibration math attempt from 3207 to 4003 mV, using MADC=593 at high end
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Mychaela Falconia <falcon@freecalypso.org>
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61 =========================================================================
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Mychaela Falconia <falcon@freecalypso.org>
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62
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63 A=(4003-3207)/(593-473)*1024 = 6792
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64
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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65 B parameter computed from each calibration point:
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66
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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67 MADC reading Voltmeter reading Computed VBAT w/o B B parameter
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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68 ---------------------------------------------------------------------------
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69 473 3207 mV 3137 70
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70 488 3306 mV 3236 70
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71 502 3403 mV 3329 74
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72 517 3500 mV 3429 71
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73 532 3597 mV 3528 69
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74 546 3696 mV 3621 75
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75 562 3804 mV 3727 77
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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76 576 3897 mV 3820 77
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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77 593 4003 mV 3933 70
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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78
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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79 B values range from 69 to 77, still a very small variation - thus we are not
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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80 too terribly sensitive to errors in the A parameter resulting from MADC values
5f9dd4056420 vbat-adc/crude-cal-test: an experiment to prove VBAT MADC linearity
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81 being on the cusp.